It has been proposed to make unauthorized duplication of a key more difficult by combining a key for actuating a lock device, such as a cylinder lock which can be mechanically locked and unlocked, with a code signal transmitter which, for instance, is provided with a light emitting element, to the end of improving the security against theft and burglary. Such a key system is disclosed in U.S. patent application No. 121,321 and now abandoned by Tanaka who is one of the joint inventors of the present application. A similar key device is proposed in U.S. Pat. No. 4,663,952 by Gelhard.
In such a key device, the electronic circuit and he power source thereof are typically incorporated in the knob provided at the base end of the key. Since the knob is required to be reasonably small for the convenience of the handling, some difficult arises in fitting the circuitry, a push-button switch, a battery and so on in the limited space in the interior of the knob. Further, since the knob is subjected to twisting torques during use, the strength of the mechanical attachment between the knob and the key is desired to be as great as possible.